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2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Rear Diff Fluid Change
I have 56,728 miles on my 2015 SL400 and decided to change out the rear differential oil. There’s no scheduled maintenance for doing that unless you have a limited slip differential. Mine is non-limited slip. To my surprise, the stuff that drained out looked like coffee (without cream and sugar). The stuff I put in was Castrol Syntrax 75W-90 and looked like golden honey.
Has anyone else change their rear differential oil and was it black?
Changing all fluids on a regular basis is good. Over the years I have changed the diff fluid on my Corvettes every 4 or 5 years and it always looks very dark. The Vettes did have limited slip.
Always hard to tell from internet pics. How’s it look lit from the back?
Fluid looks “ok” not new. I’ve seen better, I’ve seen worse. No metal shavings picked up by strong magnet right?
You could get it tested if in doubt….
Driving a car hard will obviously create a little more wear and 2nd hand cars can be a mystery. You never really know if someone replaced it, used an additive or wrong oil.
For what it’s worth, when I swapped my stock diff for the 471-LSD and drained the oil at 45k, it looked pretty close to that, maybe a little cleaner. As mentioned, internet pics are always hard to compare, colors on LCD screens look different from screen to screen.
Good Luck
Last edited by crconsulting; Jun 22, 2025 at 10:06 AM.
As long as you’re not getting metal you should be good. I know MB has used an assembly lube on non LSD diffs in the past. Some bearings will also come pre-packed for assembly, or to hold them in place. A little too much of that assembly lube may darken fluid. (especially if it’s Moly based)
I’ve used this stuff in the past on roller bearing assemblies. Great product….
JettaRed, How much fluid is required for our cars? Also, are the diffs limited slip? I'm waiting on FCP Euro to tell me what fluid they recommend? Seems MB has changed the recommended weights, is this correct?
LOL! Talk about regurgitating this discussion. We must all be getting old because I posted several times in that thread and forgot all about it. NOW I know why I had the Castrol Syntrax Long Life and Mobil DELVAC 1 in my garage!
Same here. I changed the fluid in my diff in 2022 and forgot all about it until I found the order I placed for the fluid. I used the Castrol Syntrax. Now I know I am getting old!
We must all be getting old because I posted several times in that thread and forgot all about it. NOW I know why I had the Castrol Syntrax Long Life and Mobil DELVAC 1 in my garage!
Originally Posted by rmorin49
Same here. I changed the fluid in my diff in 2022 and forgot all about it until I found the order I placed for the fluid. I used the Castrol Syntrax. Now I know I am getting old!
LOL! R231 owner demographics…
Now you know why WE aren’t a targeted demographic by Mercedes anymore.
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
R231 owner demographics…
